Highly selective alicyclic polyamide nanofiltration membrane and making method thereof

ABSTRACT

The present invention discloses a highly selective alicyclic polyamide nanofiltration membrane and a making method thereof. The method comprises the following steps: alternately and uniformly coating at least an alicyclic acid chloride solution and at least an alicyclic amine solution on a porous support membrane, using a spin coating method or a soaking method, to form at least one layer of the alicyclic polyamide nanofiltration membrane. Preferred embodiments exhibit improved ion selectivity, e.g. increased water flux, enhanced divalent/monovalent rejection selectivity, reduced fouling and improved divalent rejection rate (Ca2+, Mg2+) compared to the traditional aromatic-alicyclic mixed-structure polyamide nanofiltration membrane and/or the whole aromatic polyamide nanofiltration membrane. Therefore, the alicyclic polyamide nanofiltration membranes made in the present invention has great application prospect in the fields of zero-liquid discharge of industrial wastewater, water softening, and produce water treatment, etc.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the Continuation-in-part of InternationalApplication No. PCT/CN2017/079628, filed on Apr. 6, 2017, which is basedupon and claims priority to Chinese Application No. 2017101275950, filedon Mar. 6, 2017, the entire contents of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to the field of membrane based separationtechnology in water treatment industries, specially relates to a highlyselective alicyclic polyamide nanofiltration membrane and making methodthereof. The said highly selective and permeable nanofiltration membranecould be used for the treatment of feed streams such as surface water,industrial wastewater, dyeing wastewater, drinking water and dairyindustry. These streams contain dissolved substances with different sizeand/or charge, particularly to such processes in which:

For the surface water system, water hardness due to dissolved Ca and Mgsalts could add the inconvenience for their usage and operation,Nanofiltration membrane can remove most of Ca, Mg and other divalentions, and simultaneously permeate monovalent ion such as sodiumpotassium chloride.

In the zero liquid discharge (ZLD) wastewater treatment process,typically for industries such as salt chemical, chlor-alkali chemical,coal chemical hydrometallurgy, and pharmaceutical industries wastewatercontaining both sodium chloride and sodium sulfate components will beencountered, and the nanofiltration membrane could substantially retainsodium sulfate and allow sodium chloride to permeate.

For the waste streams generated during textile dying process, both dyesand salts are present commonly, nanofiltration membrane could be used tokeep the valuable salts while concentrating dyes into a more manageablevolume.

In drinking water supply system, the raw water may contain dissolvingand/or dispersing bacteria, assimilable Organic Carbon (AOC), volatileorganic compounds (VOCs), phthalate esters (PAEs), endocrine disruptors(EDCs), Natural (NOM) and/or Dissolved Organics (DOC) such as atrazineand/or simazine, and other trace organic pollutants (i.e. havingmolecular weights greater than about 300 Daltons), nanofiltrationmembrane could be used to remove these impurities and selectively keepsubstances that are beneficial in drinking water.

In the dairy industry, nanofiltration membrane could be used todemineralize whey products by passing undesirable monovalent salts (Na,K, and Cl) and simultaneously concentrating constituents such aslactose, protein, and calcium.

By way of examples without limitation:

Surface water may be separated with a variety of such nanofiltrationmembranes into a permeate containing primarily water and sodium andpotassium chlorides (and other monovalent salt) and a retentate sidecontaining multivalent salt in which one of the ionic moieties thereofhas two or more electric charges;

Industrial wastewater containing sodium sulfate and sodium chloride maybe separated into a permeate containing primarily water and sodiumchloride and a retentate containing sodium sulfate;

Textile printing and dyeing wastewater may be separated into a permeatecontaining primarily water and sodium chloride and a retentatecontaining valuable dyes;

Drinking water may be separated with a permeate containing primarilywater and a retentate containing low molecular organics generally havingmolecular weights in excess of about 300 Daltons.

Using the novel, alicyclic polyamide thin film composite nanofiltrationmembranes disclosed herein, the above mentioned and other separationscan be carried out with substantially separation precision and sizescreening effect as well as high water fluxes compared to thatexperienced with commercial available membranes.

BACKGROUND

Membrane separation technology solves the growing problem of clean watersupply issues in the world, with the advantages of less raw materialsand energy consumption, small foot print and free of pollution. Commonlyused water treatment membranes are divided into microfiltrationmembrane; ultrafiltration membrane; nanofiltration membrane and reverseosmose membrane. Within nanofiltration membrane could be divided intotwo categories: a class of pressured driven membrane with highselectiveness (high monovalent/divalent selectivity), referring to as ahighly selective nanofiltration membrane; and a water softeningnanofiltration membrane commonly used for removing calcium andmagnesium. With its high Ca and Mg removal rates, the latter is alsoknown as “loose” reverse osmose membrane.

The highly selective nanofiltration membrane normally has a rejectionwith molecular weight cut-off of 200-300 dalton and a pore diameter of0.1-2 nm, thus, it is widely used in the zero-liquid discharge processsuch as coal chemical plant and power plant wastewater treatment, dyeingindustry, food processing and medicine manufacture wastewater treatmentand wastewater recycling areas to selectively remove the molecules andions according to such sieve effect.

In recent years, the technology of salt separation in zero-liquiddischarge process has put forward higher requirements on the performanceof nanofiltration membranes. Membranes with defined pore sizedistribution, controlled thickness of the morphology, high desalinationselectivity, and high throughput have become a new direction ofinvention. As commonly known, the existing commercial “loose” reverseosmose membrane is prepared by interfacial polymerization of TMC(trimesoyl chloride) and MPD (metaphenylene diamine). Though having highCa and Mg removal rates, the roughness of this membrane is often high,in the range of 40-200 nm, which results poor anti-fouling performance.Therefore, improving the membrane fabrication technology, and exploringnew interfacial polymerization monomers to prepare next generation ofnanofiltration membranes becomes even more important.

At present, highly selective nanofiltration membranes are based on theclassical interfacial polymerization of TMC and anhydrous piperazine(PIP) monomers, and have an aromatic and alicyclic mixed structure. Notbonding to a standard, the specific preparation steps are as following:firstly, soaking a porous support in an aqueous phase amine solution,removing the extra aqueous amine phase or solution on the surface of theporous support by gas purging or roller-push sweeping, and thenimmersing the porous support in the organic acid chloride solution forenough reaction time, taking out the porous support to obtain ananofiltration membrane with a thickness of 20-200 nm.

Although above conventional interfacial polymerization process canproduce nanofiltration membranes with excellent desalinationperformance, it may not easily control the kinetics of the interfacialpolymerization, which influences the external morphology (thickness,roughness, surface functionality) and the internal structure (chemicalcomposition, molecular topology, molecular uniformity) of the membranes,and subsequently, have an effect on the membrane performance such aswater flux, salt rejection, and selectivity of water and salt. Duringthe removal of extra raw materials, roller-push sweeping or gas purgingis usually used in the conventional interfacial polymerization processto remove the residual aqueous phase monomers and organic monomers. Thedistribution of the aqueous phase monomers and organic monomers on theultrafiltration membrane surface or inside the surface pore could be farfrom uniform due to the instantaneous characteristics of polymerizationreaction. Thus the interfacial polymerization could be carried out in anuncontrollable manner (monomer diffusion-reaction mechanism), andtherefore the morphology and thickness of the membranes are not uniform,which affects the desalination performance of the nanofiltrationmembranes.

Nanofiltration membranes prepared by TMC and PIP monomers normally showsa certain degree of monovalent salts rejection. For example, therejection rate of NaCl is often more than 40% while Na₂SO₄, rejectionrate is greater than 95%, thus multivalent salts and monovalent saltscannot be separated completely. As a reference, during the preparationof micro-mesoporous materials such as metal-organic framework materials(MOFs), covalent organic framework materials (COFs), porous organiccages (POCs) and polymers with intrinsic microporosity, nanoporousmaterials are usually formed by designed monomers with a uniqueconfiguration through covalent bond or coordinate covalent bond,producing a unique molecular sieve separation effect on a nanoscale. Incontrast, the nanoporous membrane formed by existing monomers such astrimesoyl chloride (TMC) and piperazine (PIP) here through interfacialpolymerization cannot achieve the high selectivity of monovalent saltsand divalent salts due to the monomer structure and reactivityheterogeneity. Therefore, their fluxes are low, and the salt rejectionselectivity is poor.

SUMMARY

The objective of the present invention is to provide a highly selectivealicyclic polyamide nanofiltration membrane and making method thereof,so as to solve the problems such as inconsistent membrane structure andmorphology, low flux, poor selectivity, and poor anti-foulingproperties, etc. which are associated with the process of makingexisting nanofiltration membrane.

In order to solve the above problems, this invention includes the stepsof:

Alternately and uniformly coating at least an alicyclic acid chloridesolution and at least an alicyclic amine solution on a porous supportmembrane using a spin coating method or a soaking method for interfacialpolymerization, cycling in turn, to form at least one layer of thealicyclic polyamide nanofiltration membrane. For multi-layer membrane,the alicyclic acid chloride solution and the alicyclic amine solutionmay be alternately coated for several times. Not bond to full cycling;the last spin-coating solution may be the alicyclic acid chloridemonomer solution or the alicyclic amine monomer solution. Thenanofiltration membrane prepared by said layer by layer assembly method(multi-layer interface reaction polymerization) may have 1-10 layers orcycles. In the preparation process, a single alicyclic acid chloridemonomer solution and a single alicyclic amine monomer solution may beused for conventional interfacial polymerization or layer by layerassembly (multi-layer interfacial polymerization) to prepare thepolyamide nanofiltration membrane. Alternatively, mixed solutions of twoor more kinds of alicyclic acid chloride monomers, and two or more kindsof alicyclic amine monomers may be used for a single interfacialpolymerization or layer by layer assembly (multi-layer interfacereaction polymerization) to prepare the alicyclic polyamidenanofiltration membrane.

Further, the soaking method may include soak-coating the alicyclic acidchloride solution or the alicyclic amine solution on the porous supportmembrane or the multi-layer alicyclic polyamide nanofiltration membranefor 2-300 s.

Furthermore, the spin coating method may include spin-coating thealicyclic acid chloride or alicyclic amine on the porous supportmembrane or the multi-layer alicyclic polyamide nanofiltration membranefor 2-300 s at 50-10,000 rpm.

The present invention uses novel alicyclic acid chloride and alicyclicamine to prepare the fully alicyclic polyamide nanofiltration membrane.Both alicyclic acid chloride monomers structure and nitrogen-containedheterocyclic alicyclic cyclic amine monomers possess with a twisted andnon-coplanar structure, which are designed in single interfacialpolymerization or layer by layer assembly. Due to the non-coplanar andtwisted structures of the both monomers, the resulting nanofiltrationmembrane prepared has the characteristics of wide distribution ofmicroporous structure, high flux, high monovalent salt permeability(monovalent salt rejection rate <30%) and low divalent salt permeability(divalent salt rejection rate >99%). Therefore, the membrane has anexcellent salt separation performance.

The present invention further uses a spin-coating method to uniformlycoat the polyamide nanofiltration membrane, so that the monomer solutionis evenly distributed inside the micropores and outside the membranesurface, and thus to make the membrane with a low roughness and auniform thickness. In addition, different spin-coating time and rotationspeed could be used to adjust the distribution of the aqueous phase ororganic monomers on the microporous membrane and the surface thereof, orthe distribution on the surface of the active layer. Thus, the degree ofthe interfacial polymerization reaction of the aqueous phase monomersand organic phase monomers on the surfaces of the membrane and theactive layer could be controlled in order to achieve the control of themorphology, structure, composition and thickness of the nanofiltrationmembrane during its preparation. Consequently, the prepared alicyclicpolyamide nanofiltration membrane would improve the divalentselectivity, monovalent selectivity and flux to overcome “tailor-made”phenomenon associated with membrane materials.

Further, the nanofiltration membrane prepared in the present inventionhas a smoother membrane with a surface roughness of less than 2 nm, andan ultra-thin film thickness of less than 50 nm.

Based on the technical solutions mentioned above, the present inventioncan also be improved as following:

Further, the process of the interfacial polymerization or layer by layerassembly, the following steps are further included:

Removing the extra alicyclic acid chloride solution or alicyclic aminesolution on the porous support membrane or the multi-layer alicyclicpolyamide nanofiltration membrane by the spin coating or soaking method,after coating the alicyclic acid chloride solution or alicyclic aminesolution on the porous support membrane or the multi-layer alicyclicpolyamide nanofiltration membrane by the soaking or spin-coating method.Wherein the extra alicyclic acid chloride solution or alicyclic aminesolution is thrown away and removed at 3,000-10,000 rpm for 2-300 s.

Further, after forming the alicyclic polyamide membrane, the followingsteps are further included:

Washing the alicyclic polyamide membrane with a low boiling organicsolvent for 15-60 s, removing the organic solvent at a rotation speed of3,000-10,000 rpm for 40-60 s, then providing a heat-treatment to thealicyclic polyamide membrane at 50-90° C. for 1-10 min to obtain thehighly selective alicyclic polyamide nanofiltration membrane. Whereinlow boiling organic solvent is one or more selected from the groupconsisting of n-hexane, cyclohexane, cyclopentane, n-heptane, n-octaneand iso-Par.

Further, a mass fraction of the alicyclic acid chloride is 0.01-2 wt %,a mass fraction of the alicyclic amine is 0.01-4 wt %.

Further, the alicyclic acid chloride solution includes an alicyclic acidchloride, an organic solvent and an additive. Wherein a mass fraction ofthe alicyclic acid chloride is 0.01-2 wt %, a mass fraction of theorganic solvent is 96-99.98 wt % and a mass fraction of the additive is0.01-2 wt %. Wherein the organic solvent is one or more selected fromthe group consisting of n-hexane, cyclohexane, cyclopentane, n-heptane,n-octane and iso-Par.

Wherein the alicyclic amine solution includes an alicyclic amine, anaqueous solvent and an additive. Wherein a mass fraction of thealicyclic amine is 0.01-4 wt %, a mass fraction of the aqueous solventis 46-99.98 wt % and a mass fraction of the additive is 0.01-50 wt %.

Further, the alicyclic acid chloride solution includes the alicyclicacid chloride and the organic solvent. Wherein the mass fraction of thealicyclic acid chloride is 0.01-2 wt %, and the mass fraction of theorganic solvent is 98-99.9 wt %;

Further, the additive is nanoparticles, an organic phenol having adistorted spatial structure, a co-solvent, a hydrophilic additive or asurfactant.

Wherein the nanoparticles are selected from the group consisting offlaky graphene, elongated single-walled carbon nanotube, elongatedmulti-walled carbon nanotube, organic spherical porous molecule,cage-shaped porous molecule, and wheel-shaped porous molecule.

Wherein the organic phenol having a distorted spatial structure is5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobiindane orfluorene-9-bisphenol. There's a large spatial structure in the phenolicstructure, which may form a more distorted polyester and polyamide blockcopolymer.

Wherein the co-solvent is selected from the group consisting of acetone,polyol, organophosphorus, dimethylsulfoxide and dimethylformamide.

Wherein the hydrophilic additive is selected from the group consistingof quaternary ammonium salt, alcohol-amine, camphorsulfonic acid andpolyvinylpyrrolidone (PVP).

Wherein the surfactant is one or more selected from the group consistingof PEG 200, PEG 400 and PEG 600.

Further, the alicyclic acid chloride has a structural formula of:

Wherein A is an alicyclic group selecting from the group consisting offour-membered ring, five-membered ring, six-membered ring,seven-membered ring and eight-membered ring. Wherein R₁, R₂, R₃ and R₄are respectively —C(O)Cl group or H, wherein the number of the —C(O)Clgroups is 3-6, wherein two —C(O)Cl groups are ortho or meta to eachother.

Wherein the used alicyclic acid chloride includes three or more“—C(O)Cl” groups bonding to the saturated alicyclic hydrocarbon, such ascyclobutene, cyclopentane and cyclohexane. The alicyclic acid chlorideused in the present invention can be one or more selected from the groupconsisting of 1,2,3,4-cyclobutanetetracarboxylic acid chloride,1,2,4,5-cyclohexanetetracarboxylic acid chloride, 1,3,5-cyclohexanetricarboxylic acid chloride, 1,2,4-cyclopentanetricarboxylic acidchloride, 1,2,3,4-cyclopentanetetracarboxylic acid chloride and 1, 2, 3,4, 5, 6-cyclohexanecarboxylic acid chloride.

Further, the alicyclic amine has a structural formula of:

Wherein R₁, R₂, are respectively —(CH₂)_(n)— or —NH—, wherein n is 1-3;wherein R₃, R₄, R₅, R₆ are respectively —NH₂ or —CH₃; wherein thenumbers of the —NH— and —NH₂ are 1-4. Wherein when the plurality of —NH₂are on the same side of the ring, both conformations of cis and transare included.

The alicyclic amine is a nitrogen-containing heterocyclic structure, inwhich two or more “—NH₂ and —NH—” are bonded to the saturated alicyclichydrocarbon or replace C of the original saturated alicyclichydrocarbon. Wherein the alicyclic amine monomers can be one or moreselected from the group consisting of 2,5-dimethylpiperazine,(1R,2R)-(−)-1,2-diaminocyclohexane, 1,2-diaminocyclohexane,2,6-dimethylpiperazine, anhydrous piperazine, cyclohexane-1,3-diamineand cyclohexane-1,4-diamine.

Further, the porous support membrane is selected from the groupconsisting of organic polymer ultrafiltration membrane, hollow fiberultrafiltration membrane, inorganic ultrafiltration membrane materialand organic-inorganic hybrid porous membrane. Wherein the organicpolymer ultrafiltration membrane is selected from the group consistingof polysulfone, polyethersulfone, polyacrylonitrile and polyimide; andthe inorganic ultrafiltration membrane material is porous alumina orporous ceramic membrane.

The present invention has the following advantages:

In the present invention, a single interfacial polymerization or layerby layer assembly (multi-layer interface reaction polymerization) iscarried out by using alicyclic acid chloride and alicyclic aminemonomers in a convenient and controllable manner to prepare a highlyselective polyamide nanofiltration membrane with low surface roughness.Under certain optimum conditions, the highly selective alicyclicpolyamide nanofiltration membrane prepared by the method has a rejectionrate of more than 99% and a rejection rate of less than 13% for Na₂SO₄and NaCl, respectively. The fluxes are 89.615 kg·m⁻²·h⁻¹·MPa⁻¹ and104.339 kg·m⁻²·h⁻¹·MPa⁻¹, respectively, showing an excellentdivalent/monovalent selectivity with a 50% increase in flux compared tothe traditional interfacial polymerization. In a test using a mixed saltsolution having a certain rejection rate, the rejection rate of thesemi-aromatic polyamide for Cl⁻¹ is about −19%, while the rejection rateof the alicyclic polyamide nanofiltration membrane prepared in thepresent invention for Cl⁻¹ is more than −38%, which indicating latterhas an extreme low monovalent rejection rate. Under another optimalcondition, removal rates of CaCl₂, MgCl₂, MgSO₄ and Na₂SO₄ of thealicyclic polyamide membrane prepared by present invention are all above99% and the fluxes are between 80-90 kg·m⁻²·h⁻¹·MPa⁻¹, with extremelylow membrane surface roughness. The alicyclic polyamide membraneprepared by the present invention is suitable for the fields of watersoftening, salt separation for zero-liquid discharge of industrialwastewater and biological medicine, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional morphology of the alicyclic polyamidenanofiltration membrane prepared in Embodiment 1 of the presentinvention;

FIG. 2 is a cross-sectional morphology of the alicyclic polyamidenanofiltration membrane Embodiment 2, prepared by the conventionalinterfacial polymerization-plate frame method;

FIG. 3 is the linear variation of the thickness of active layers varyingwith the number of layers, wherein the test data of thickness are fromthe ellipsometer;

FIG. 4 shows the rejection effects of the alicyclic polyamidenanofiltration membrane prepared in Embodiment 1 of the presentinvention and rejection effects of the commercial semi-aromaticpolyamide nanofiltration membrane for SO₄ ²⁻ and Cl⁻¹ with differentconcentrations. The test conditions are as follows: salts used are NaCland Na₂SO₄, wherein the Cl⁻¹ and SO₄ ²⁻ are of the same molarconcentration, having a total ion molar concentrations of 14.04 mol·m⁻³,28.08 mol·m⁻³, 56.16 mol·m⁻³, 84.24 mol·m⁻³, 112.32 mol·m⁻³, 140.04mol·m⁻³, and 168.48 mol·m⁻³, and the test pressure is 1 MPa, thetemperature is 25° C., and a flow rate is 7 LPM.

DETAILED DESCRIPTION

The principle and features of the present invention are described belowwith reference to the accompanying drawings. The illustrated embodimentsare only used to explain the present invention, and are not intended tolimit the scope of the present invention.

Embodiment 1

A method of making a highly selective alicyclic polyamide nanofiltrationmembrane, including the steps of:

-   -   (1) Coating a layer of the alicyclic amine solution on a        polyethersulfone ultrafiltration membrane by spin-coating        method. Specially, allowing the piperazine solution to stand on        the membrane for 120 s, throwing away the alicyclic amine        solution by the spin-coating method at a rotation speed of        10,000 rpm for 40 s. Wherein the alicyclic amine solution        includes a piperazine, an aqueous solvent and an additive.        Wherein the additive is acetone and the aqueous phase solvent is        water. Wherein a mass fraction of the piperazine is 1.5 wt %, a        mass fraction of the acetone is 0.1 wt % and a mass fraction of        the water is 98.4 wt %.    -   (2) Coating a layer of the alicyclic acid chloride solution on        the polyethersulfone ultrafiltration membrane coated with the        alicyclic amine solution obtained in step (1) by the        spin-coating method for interfacial polymerization, with a        spin-coating time of 10 s and a rotation speed of 300 rpm. Then        throwing away the extra alicyclic acid chloride solution by the        spin-coating method at a rotation speed of 10,000 rpm for 40 s.        Wherein the alicyclic acid chloride solution includes a 1, 3,        5-cyclohexane tricarboxylic acid chloride and an organic        solvent, wherein the organic solvent is n-hexane. A mass        fraction of the 1, 3, 5-cyclohexanetricarboxylic acid chloride        is 0.1 wt % by weight, and a mass fraction of the organic        solvent is 99.9 wt % by weight;    -   (3) Washing the alicyclic polyamide nanofiltration membrane        obtained in step (2) with n-hexane for 15 s, removing the        n-hexane at a rotation speed of 3,000 rpm for 40 s, then        providing a heat-treatment to the alicyclic polyamide        nanofiltration membrane at 50° C. for 60 s to obtain the highly        selective alicyclic polyamide nanofiltration membrane, and the        cross-section thereof is shown in FIG. 1.    -   (4) For comparison, a series of equal molar concentration of        Cl⁻¹ and SO₄ ²⁻ were used to test the desalination performance        of the above alicyclic polyamide membrane and the commercial        semi-aromatic polyamide membrane. The comparison curve is shown        in FIG. 4.

Embodiment 2

Preparing the alicyclic polyamide nanofiltration membrane by interfacialpolymerization method, including the following steps:

-   -   (1) Soaking a polyethersulfone ultrafiltration membrane in an        alicyclic amine solution, and taking the polyethersulfone        ultrafiltration membrane out after 120 s; gas purging the        surface of the ultrafiltration membrane to remove the extra        alicyclic amine solution. Wherein the alicyclic amine solution        is composed of piperazine, additive and aqueous phase solvent.        Wherein the additive is acetone, the aqueous phase solvent is        water. Wherein a mass fraction of the piperazine is 1.5 wt %, a        mass fraction of the acetone is 0.1 wt %, and a mass fraction of        the aqueous solvent is 98.4 wt %;    -   (2) Soaking a 1, 3, 5-cyclohexanetricarboxylic acid chloride        solution on the ultrafiltration membrane with the piperazine        solution on the surface obtained in the step (1), and taking the        ultrafiltration membrane out after 10 s; wherein the organic        solvent is n-hexane. Wherein a mass fraction of the 1, 3,        5-cyclohexanetricarboxylic acid chloride is 0.1 wt %, and a mass        fraction of organic solvent is 99.9 wt %;    -   (3) Washing the alicyclic polyamide nanofiltration membrane        obtained in step (2) with n-hexane for 15 s, then providing a        heat-treatment to the alicyclic polyamide nanofiltration        membrane at 50° C. for 60 s, similarly to that of Embodiment 1,        to obtain the highly selective alicyclic polyamide        nanofiltration membrane.

The cross-sectional view of Embodiment 2 is shown in FIG. 2. It can beseen from FIG. 1 and FIG. 2 that the alicyclic polyamide nanofiltrationmembrane prepared by the conventional interfacial polymerization-plateframe method has a consistent cross-sectional morphology, while that ofthe alicyclic polyamide nanofiltration membrane prepared by thespin-coating method is composed of a porous supporting layer and anactive layer. The comparison of the desalination performances of thealicyclic polyamide nanofiltration membranes prepared by theconventional interfacial polymerization-plate frame method and thespin-coating method used in Embodiment 1 of the present invention isshown in FIG. 3. As can be seen in FIG. 3, both the rejection rates ofMg₂SO₄ by the nanofiltration membrane prepared by the interfacialpolymerization spin-coating method and the nanofiltration membraneprepared by the interfacial polymerization-plate frame method remainabove 97%, within a polymerization time of 5-30 s. The nanofiltrationmembrane prepared by the interfacial polymerization-spin-coating methodhas a 20-40% increase in membrane flux compared to the nanofiltrationmembrane prepared by the interfacial polymerization-plate frame method,at different interfacial polymerization periods.

The rejection rates of the alicyclic polyamide nanofiltration membraneprepared in Embodiment 1 and the alicyclic polyamide nanofiltrationmembrane prepared in Embodiment 2 for various types of salts arerespectively tested. Wherein the test conditions are as follows:cross-flow test, a single salt concentration of 2,000 ppm, 25° C., 1MPa, and a flow rate of 7 LPM. The details of the test are shown inTable 1 and Table 2.

TABLE 1 Salt rejection properties of the alicyclic polyamidenanofiltration membrane prepared in Embodiment 1 for salts Na₂SO₄ MgSO₄CaCl₂ NaCl KCl Rejection rate (%) 98.97 ± 0.04 97.77 ± 0.07 65.15 ± 0.0815.47 ± 0.15 18.49 ± 0.39 Membrane Flux 62.41 ± 0.29 60.45 ± 0.43 53.70± 0.42 63.55 ± 0.63 65.83 ± 0.33 (kg · m⁻² · h⁻¹ · MPa⁻¹)

TABLE 2 Salt rejection properties of the alicyelic polyamidenanofiltration membrane prepared in Embodiment 2 for salts Na₂SO₄ MgSO₄CaCl₂ NaCl KCl Rejection rate (%) 97.58 ± 0.29 96.83 ± 0.32 64.17 ± 0.1516.04 ± 0.28 19.27 ± 0.42 Membrane Flux  42.8 ± 1.97  41.8 ± 1.37  36 ±2.3  46.3 ± 1.97  47.2 ± 1.52 (kg · m⁻² · h⁻¹ · MPa⁻¹)

As can be seen from Table 1 and Table 2, rejection abilities of thealicyclic polyamide nanofiltration membrane for different salts are:Na₂SO₄>MgSO₄>CaCl₂>KCl>NaCl. Referring to Table 1, the rejection ratefor the divalent salt Na₂SO₄ is more than 98.97%, while the rejectionrate for monovalent salts of NaCl and KCl are respectively 15.47% and18.49%, showing an excellent selective permeability differences betweenthe monovalent salt and bivalent salt. As to the flux, the fluxes of thealicyclic polyamide membrane to different salts areKCl>NaCl>Na₂SO₄>MgSO₄>CaCl₂. Wherein the flux of the monovalent salt isgreater than that of the divalent salt due to the different radii ofhydration ions of different salt solutions, resulting in osmoticpressure difference on both sides of the diaphragm during infiltration.Comparison of Table 1 and Table 2 shows that the rejection rates of thealicyclic polyamide prepared by the interfacial polymerizationspin-coating method and the interfacial polymerization-plate-framemethod do not differ much. While the flux of the interfacialpolymerization spin-coating method is higher than that of the latter.

Embodiment 3

A method of making a highly selective alicyclic polyamide nanofiltrationmembrane, including the steps of:

-   -   (1) Coating a layer of the alicyclic amine solution on a        polyethersulfone ultrafiltration membrane by spin-coating        method. Specially, spin-coating a mixed alicyclic amine solution        including piperazine and graphene oxide on the membrane at a        speed of 500 rpm for 10 s, throwing away the alicyclic amine        solution by the spin-coating method at a rotation speed of 9,000        rpm for 30 s. Wherein the alicyclic amine solution is composed        of piperazine, aqueous solvent and additive. Wherein a mass        fraction of the graphene oxide is 0.05 wt %, a mass fraction of        the piperazine is 2 wt % and a mass fraction of the aqueous        solvent is 97.95 wt %.    -   (2) Coating a layer of the alicyclic acid chloride solution on        the polyethersulfone ultrafiltration membrane coated with the        alicyclic amine solution obtained in step (1) by the        spin-coating method for interfacial polymerization. Specially,        spin-coating the alicyclic acid chloride solution on the        membrane at 500 rpm for 10 s. Then throwing away the extra        alicyclic acid chloride solution by the spin-coating method at a        rotation speed of 3,000 rpm for 40 s. Wherein the alicyclic acid        chloride solution is composed of 1, 2, 4,-cyclopentane        tricarboxylic acid chloride and organic solvent, wherein the        organic solvent is n-heptane. Wherein a mass fraction of the 1,        2, 4,-cyclopentane tricarboxylic acid chloride is 0.01 wt %, and        a mass fraction of the n-heptane is 99.99 wt %.    -   (3) Washing the alicyclic polyamide nanofiltration membrane        obtained in step (2) with n-hexane for 60 s, removing the        n-hexane at a rotation speed of 10,000 rpm for 60 s, then        providing a heat-treatment to the alicyclic polyamide        nanofiltration membrane at 90° C. for 2 min to obtain the highly        selective alicyclic polyamide nanofiltration membrane.

The desalination performance of the alicyclic polyamide nanofiltrationmembrane prepared using the graphene oxide as aqueous solvent in thisembodiment is tested. The test conditions are as following:cross-current test, a single salt concentration of 2,000 ppm, 25° C., 1MPa, and a flow rate of 7 LPM. The details of the test are shown inTable 3.

TABLE 3 Effects of graphene oxide as an aqueous additive on thedesalination performance Graphene oxide-based alicyclic alicyclicpolyamide polyamide nanofiltration membrane nanoflitration membraneRejection rate Membrane Flux Rejection rate Membrane Flux (%) (kg · m⁻²· h⁻¹ · MPa⁻¹) (%) (kg · m⁻² · h⁻¹ · MPa⁻¹) Na₂SO₄ 98.90 89.615 98.9556.56 NaCl 12.53 ± 0.58 104.34 ± 3.74 15.49 ± 0.4 67.61 ± 2.5

As can be seen from Table 3, the alicyclic polyamide nanofiltrationmembrane added with graphene oxide shows lower monovalent salt rejectionrate and higher flux than that of the non-added alicyclic polyamidenanofiltration membrane, and the rejection rate of divalent salt remainsunchanged. In particular, the rejection rates of Na₂SO₄ and NaCl forgraphene oxide-based alicyclic polyamide nanofiltration membranes are98.90% and 12.53%, respectively; and the fluxes are 89.62 and 104.34kg·m⁻²·h⁻¹·MPa⁻¹, respectively. Compared the performance of alicyclicpolyamide nanofiltration membrane made without the addition of grapheneoxide, the fluxes of monovalent and divalent salts increase by 55% and58%, respectively. While the monovalent salt rejection rate dropped to12.53% and the rejection rate of divalent salt remains unchanged.

Embodiment 4

A method of making a highly selective alicyclic polyamide nanofiltrationmembrane, including the steps of:

-   -   (1) Coating a layer of alicyclic amine solution on a        polyacrylonitrile ultrafiltration membrane by spin-coating        method. Specially, spin-coating an alicyclic amine solution on        the membrane at a speed of 50 rpm for 5 s, throwing away the        alicyclic amine solution at a rotation speed of 10,000 rpm for        10 s. Wherein the alicyclic amine solution is composed of        trans-1, 4-cyclohexanediamine, camphorsulfonic acid and water.        Wherein a mass fraction of the trans-1, 4-cyclohexanediamine is        2 wt %, a mass fraction of the camphorsulfonic acid is 0.5 wt %        and a mass fraction of the water is 97.5 wt %.    -   (2) Coating a layer of alicyclic acid chloride solution on the        polyacrylonitrile ultrafiltration membrane coated with the        alicyclic amine solution obtained in step (1) by spin-coating        method for interfacial polymerization. Specially, spin-coating        the alicyclic acid chloride solution on the membrane at 500 rpm        for 20 s. Then throwing away the extra alicyclic acid chloride        solution at a rotation speed of 3,000 rpm for 60 s. Wherein the        alicyclic acid chloride solution is composed of 1, 2, 3,        4-cyclobutane tetracarboxylic acid chloride and organic solvent,        wherein the organic solvent is n-heptane. Wherein a mass        fraction of the 1, 2, 3, 4-cyclobutane tetracarboxylic acid        chloride is 0.38 wt %, and a mass fraction of the n-heptane is        99.62 wt %.    -   (3) Washing the alicyclic polyamide nanofiltration membrane        obtained in step (2) with cyclohexane for 120 s, and removing        the cyclohexane at a rotation speed of 7,000 rpm for 50 s.    -   (4) Repeating step (1), step (2) and step (3) to obtain the        alicyclic polyamide nanofiltration membrane prepared by the        layer by layer assembly method, then providing a heat-treatment        to the alicyclic polyamide nanofiltration membrane at 70° C. for        5 min to obtain the highly selective alicyclic polyamide        nanofiltration membrane.

The desalination performance, for Na₂SO₄ and NaCl, of the alicyclicpolyamide nanofiltration membrane prepared by four cycles of layer bylayer assemblies, using the 1, 2, 3, 4-cyclobutane tetracarboxylic acidchloride as the alicyclic acid chloride solution, in this embodiment istested. The test conditions are as following: cross-current test, asingle salt concentration of 2,000 ppm, 25° C., 1 MPa, and a flow rateof 7 LPM. The details of the test are shown in Table 4.

TABLE 4 Salt rejection properties of the 1,2,3,4-cyclobutanetetracarboxylic acid chloride-based alicyclic polyamide nanofiltrationmembrane Na₂SO₄ NaCl Rejection rate Membrane Flux Rejection rateMembrane Flux (%) (kg · m⁻² · h⁻¹ · MPa⁻¹) (%) (kg · m⁻² · h⁻¹ · MPa⁻¹)1 layer 86.35% 90.20 12.84% 118.41 2 layers 94.36% 82.93 13.70% 101.84 3layers 96.27% 75.38 14.25% 91.76 4 layers 98.51% 72.40 15.01% 85.32

As can be seen from Table 4, the rejection rates of Na₂SO₄ and NaCl forthe alicyclic polyamide nanofiltration membranes prepared by layer bylayer assembly method are 98% and 15%, respectively. And with theincrease of the number of layers, the rejection rate of Na₂SO₄ increasesfrom 86.35% to 98.51%; while the rejection rate of NaCl increases from12.84% to 15.01%, which remains nearly unchanged. At the same time, withthe increase of the number of layers, the flux of the alicyclicpolyamide nanofiltration membranes prepared by the layer by layerassembly method decreases as expected. When the layers increases from 1to 4, the flux for Na₂SO₄ decreased from 90.20 kg·m⁻²·h⁻¹·MPa⁻¹ to72.40·kg·m⁻²·h⁻¹·MPa⁻¹, while the flux for NaCl decreases from 118.41kg·m⁻²·h⁻¹·MPa⁻¹ to 85.32 kg·m⁻²·h⁻¹·MPa⁻¹. Thus, alicyclic polyamidenanofiltration membranes with different layers show controllablecharacteristics on the rejection rate and flux, that is, the layer bylayer can be assembled to adjust and regulate the performance of thenanofiltration membrane.

Embodiment 5

A method of making a highly selective alicyclic polyamide nanofiltrationmembrane, including the steps of:

-   -   (1) Coating a layer of alicyclic amine solution on a        polyethersulfone ultrafiltration membrane by soaking method.        Specially, allowing the alicyclic amine solution to stand on the        polyethersulfone membrane for 240 s, throwing away the alicyclic        amine solution at a rotation speed of 3,000 rpm for 60 s.        Wherein the alicyclic amine solution is composed of trans-1,        4-cyclohexanediamine and water. Wherein a mass fraction of the        trans-1, 4-cyclohexanediamine is 3 wt %, a mass fraction of the        water is 97 wt %.    -   (2) Coating a layer of alicyclic acid chloride solution on the        polyethersulfone ultrafiltration membrane coated with the        alicyclic amine solution obtained in step (1) by spin-coating        method for interfacial polymerization. Specially, allowing the        alicyclic acid chloride solution to stand on the ultrafiltration        membrane for 60 s, then throwing away the extra alicyclic acid        chloride solution at a rotation speed of 8,000 rpm for 50 s.        Wherein the alicyclic acid chloride solution is composed of a 1,        2, 4, 5-cyclohexane tetracarboxylic acid chloride, an organic        solvent and an additive, wherein the additive is acetone and the        organic solvent is n-heptane. Wherein a mass fraction of the 1,        2, 4, 5-cyclohexane tetracarboxylic acid chloride is 0.12 wt %,        a mass fraction of the acetone is 1 wt % and a mass fraction of        the n-heptane is 98.88 wt %.    -   (3) Washing the alicyclic polyamide nanofiltration membrane        obtained in step (2) with cyclohexane for 120 s, removing the        cyclohexane at a rotation speed of 10,000 rpm for 60 s.    -   (4) Soaking the washed alicyclic polyamide nanofiltration        membrane in a 3 wt % isopropanol-water solution for 3 min, then        providing a heat-treatment to the alicyclic polyamide        nanofiltration membrane at 90° C. for 5 min to obtain the highly        selective alicyclic polyamide nanofiltration membrane.

The rejection rates test of the alicyclic polyamide nanofiltrationmembrane prepared in this embodiment are performed on various types ofsalts. The test conditions are as follows: cross-current test, a singlesalt concentration of 2,000 ppm, 25° C., 1 MPa, and a flow rate of 7LPM. The details of the test are shown in Table 5.

TABLE 5 Salt rejection properties of the alicyclic polyamidenanofiltration membrane prepared using 1,2,4,5-cyclohexanetetracarboxylic acid chloride for various types of salts Na₂SO₄ MgSO₄CaCl₂ NaCl MgCl₂ Rejection rate (%) 95.14 ± 0.23 93.4 ± 0.2 87.15 ± 0.4520.71 ± 0.76 93.37 ± 0.35 Membrane Flux 48.69 ± 0.83 46.10 ± 0.42 40.18± 0.98 45.78 ± 0.73 43.33 ± 0.74 (kg · m⁻² · h⁻¹ · MPa⁻¹)

As can be seen from Table 5, both the flux and rejection rate of thealicyclic polyamide nanofiltration membranes prepared from 1, 2, 4,5-cyclohexanetetracarboxylic acid chloride and trans-1,4-cyclohexanediamine are lower than that of the alicyclic polyamidenanofiltration membranes prepared from 1, 3, 5-cyclohexane tricarboxylicacid chloride and piperazine. Specifically, the flux of thenanofiltration membrane for Na₂SO₄ is 48.69 kg·m⁻²·h⁻¹·MPa⁻¹, and therejection rate of Na₂SO₄ is 95.14%; meanwhile, the flux for NaCl is45.78±0.73 kg·m⁻²·h⁻¹·MPa⁻¹ and the rejection rate of NaCl is 20.71%.Thus, it is further demonstrated that invented alicyclic polyamidenanofiltration membranes are highly selective toward the saltseparation.

Embodiment 6

A method of making a highly selective alicyclic polyamide nanofiltrationmembrane, including the steps of:

-   -   (1) Coating a layer of alicyclic amine solution on a        polyethersulfone ultrafiltration membrane by plate frame method.        Specially, soak-coating the alicyclic amine solution to stand on        the polyethersulfone membrane for 120 s, removing the extra        aqueous phase solution by gas purging or roller squeezing.        Wherein the alicyclic amine solution is composed of piperazine        and an aqueous phase solution, wherein the aqueous phase        solution is water. Wherein a mass fraction of the piperazine is        3.2 wt %, a mass fraction of the water is 96.8 wt %.    -   (2) Coating a layer of alicyclic acid chloride solution on the        polyethersulfone ultrafiltration membrane containing the        piperazine on the surface, obtained in step (1) for interfacial        polymerization. Specially, coating the alicyclic acid chloride        solution on the membrane containing piperazine molecules and        standing for reaction for 30 s, then removing the extra        alicyclic acid chloride solution. Wherein the alicyclic acid        chloride solution is composed of a 1, 2, 3, 4-cyclobutane formic        acid chloride and an organic solvent. Wherein a mass fraction of        the 1, 2, 3, 4-cyclobutane formic acid chloride is 0.32 wt %.        Wherein the organic solvent is n-hexane and a mass fraction of        the n-hexane is 99.68 wt %.    -   (3) Washing the alicyclic polyamide nanofiltration membrane        obtained in step (2) with n-hexane for 40 s, then providing a        heat-treatment to the alicyclic polyamide nanofiltration        membrane at 60° C. for 2 min to obtain the highly selective        alicyclic polyamide nanofiltration membrane.

The rejection rates test of the alicyclic polyamide nanofiltrationmembrane prepared in this embodiment are performed on various types ofsalts. The test conditions are as following: cross-current test, asingle salt concentration of 2,000 ppm, 25° C., 1 MPa, and a flow rateof 7 LPM. The details of the test are shown in Table 6.

TABLE 6 Salt rejection properties of the alicyclic polyamidenanofiltration membrane prepared by interfacial polymerization methodfor various types of salts. Na₂SO₄ MgSO₄ CaCl₂ NaCl MgCl₂ Rejection rate(%) 99.1 ± 0.13 99.4 ± 0.04 99.1 ± 0.11 83.3 ± 0.54 99.1 ± 0.31 MembraneFlux 86.8 ± 0.61 88.3 ± 0.24 84.6 ± 0.91 96.7 ± 0.30 82.9 ± 0.82 (kg ·m⁻² · h⁻¹ · MPa⁻¹)

As can be seen from Table 6, the rejection abilities of the alicyclicpolyamide nanofiltration membrane prepared from 1, 2, 3, 4-cyclobutaneformic acid chloride for different salts are:Na₂SO₄═MgSO₄═CaCl₂═MgCl₂>NaCl. Wherein the rejection rate of thealicyclic polyamide nanofiltration membrane prepared from this kind ofacid chloride for all divalent salts is more than 99%, and the rejectionrate for the monovalent salt is 83.3%, and the flux is 82.9-96.7kg·m⁻²·h⁻¹·MPa⁻¹.

Embodiment 7

A method of making a highly selective alicyclic polyamide nanofiltrationmembrane, including the steps of:

-   -   (1) Coating a layer of alicyclic amine solution on a polyimide        ultrafiltration membrane by spin-coating method. Specially,        allowing an alicyclic amine solution to stand on the membrane        for 180 s, throwing away the alicyclic amine solution at a        rotation speed of 5,000 rpm for 30 s. Wherein the alicyclic        amine solution is composed of reduced graphene oxide, piperazine        and water. Wherein a mass fraction of the reduced graphene oxide        is 0.1 wt %, a mass fraction of the piperazine is 2 wt %, and a        mass fraction of the water is 97.9 wt %.    -   (2) Coating a layer of the alicyclic acid chloride solution on        the polyimide ultrafiltration membrane coated with the alicyclic        acid chloride solution obtained in step (1) by spin-coating        method for interfacial polymerization. Specially, allowing the        alicyclic acid chloride solution to stand on the membrane coated        with the alicyclic amine solution for 5 s, throwing away the        extra alicyclic acid chloride solution at a rotation speed of        3,000 rpm for 40 s. Wherein the alicyclic acid chloride solution        includes a 1, 3, 5-cyclohexane tricarboxylic acid chloride,        additive and an organic solvent. Wherein the additive is        lutidine and the organic solvent is cyclohexane. Wherein a mass        fraction of the 1, 3, 5-cyclohexane tricarboxylic acid chloride        is 0.2 wt %, a mass fraction of the lutidine is 1 wt % and a        mass fraction of cyclohexane is 98.8 wt %.    -   (3) Washing the alicyclic polyamide nanofiltration membrane        obtained in step (2) with n-hexane for 60 s, removing the        n-hexane at a rotation speed of 10,000 rpm for 60 s, then        providing a heat-treatment to the alicyclic polyamide        nanofiltration membrane at 60° C. for 2 min to obtain the highly        selective alicyclic polyamide nanofiltration membrane.    -   (4) Repeating the above steps to obtain alicyclic polyamide        nanofiltration membranes with different layers.

The desalination performance of the alicyclic polyamide nanofiltrationmembrane prepared, using the reduced graphene oxide as aqueous solventin this embodiment is tested. The test conditions are as following:cross-current test, a single salt concentration of 2,000 ppm, 25° C., 1MPa, and a flow rate of 7 LPM. The details of the test are shown inTable 7.

TABLE 7 Rejection properties of the alicyclic polyamide nanofiltrationmembrane prepared from the reduced graphene oxide for Na₂SO₄ and NaClNa₂SO₄ NaCl Rejection rate Membrane Flux Rejection rate Membrane Flux(%) (kg · m⁻² · h⁻¹ · MPa⁻¹) (%) (kg · m⁻² · h⁻¹ · MPa⁻¹) 1 layer 99.03%97.23 11.15 ± 0.17% 106.61 ± 2.62 2 layers 99.28% 89.24 11.64 ± 0.28%101.29 ± 1.75 3 layers 99.38% 81.37 12.03 ± 0.91%  94.82 ± 2.83 4 layers99.71% 76.38 12.48 ± 0.72%    90 ± 1.39

As can be seen from Table 7, as compared to Embodiment 1, the alicyclicpolyamide nanofiltration membrane added with the reduced graphene oxideshows a lower monovalent salt rejection rate and a higher flux than thenon-added alicyclic polyamide nanofiltration membrane. The rejectionrate of the divalent salt remains unchanged. In particular, when thenumber of layer by layer assembly layers increases from 1 layer to 4layers, the rejection rate of the alicyclic polyamide nanofiltrationmembrane for Na₂SO₄ does not change much, all of which are maintained atover 99%, whereas the flux decreases from 97.23 kg·m⁻²·h⁻¹·MPa⁻¹ to76.38 kg·m⁻²·h⁻¹·MPa⁻¹. The rejection rates of NaCl are all below 12%,whereas flux for NaCl decreases from 106.61 kg·m⁻²·h⁻¹·MPa⁻¹ to 90kg·m⁻²·h⁻¹·MPa⁻¹. Thus, the above results demonstrate that alicyclicpolyamide nanofiltration membranes with different layers prepared bylayer by layer assembly method exhibit controllable rejection rates andfluxes, that is, the active layer can be assembled to adjust andregulate the performance of the nanofiltration membrane.

Embodiment 8

A method of making a highly-selective alicyclic polyamide nanofiltrationmembrane, including the steps of:

-   -   (1) Coating a layer of alicyclic amine solution on a        polyethersulfone ultrafiltration membrane by soaking method.        Specially, allowing an alicyclic amine solution to stand on the        polyethersulfone membrane for 120 s, removing the extra        alicyclic amine solution by gas purging or roller squeezing.        Wherein the alicyclic amine solution is composed of trans-1,        4-cyclohexanediamine and water. Wherein a mass fraction of the        trans-1, 4-cyclohexanediamine is 2 wt % and a mass fraction of        the water is 98 wt %.    -   (2) Interfacial polymerizing the polyethersulfone        ultrafiltration membrane coated with the alicyclic amine        solution obtained in step (1) with an alicyclic acid chloride        solution.

Specially, allowing the alicyclic acid chloride solution to stand on theultrafiltration membrane obtained in step (1) for 30 s, then throwingaway the extra alicyclic acid chloride solution at a rotation speed of8,000 rpm for 50 s. Wherein the alicyclic acid chloride solution iscomposed of a 1, 3, 5-cyclohexane tricarboxylic acid chloride and anorganic solvent. Wherein the organic solvent is cyclohexane. Wherein amass fraction of the 1, 3, 5-cyclohexane tricarboxylic acid chloride is0.2 wt % and a mass fraction of the cyclohexane is 99.8 wt %.

-   -   (3) Washing the alicyclic polyamide nanofiltration membrane        obtained in step (2) with n-hexane for 120 s, removing the        n-hexane at a rotation speed of 10,000 rpm for 60 s    -   (4) Soaking the washed alicyclic polyamide nanofiltration        membrane in a 3 wt % isopropanol—water solution for 3 min, then        providing a heat-treatment to the alicyclic polyamide        nanofiltration membrane at 70° C. for 5 min to obtain the highly        selective alicyclic polyamide nanofiltration membrane.

The rejection rates, for various types of salts, of the alicyclicpolyamide nanofiltration membrane prepared in this embodiment aretested. The test conditions are as following: cross-current test, asingle salt concentration of 2,000 ppm, 25° C., 1 MPa, and a flow rateof 7 LPM. The details of the test are shown in Table 8.

TABLE 8 Salt rejection properties of the alicyclic polyamidenanofiltration membrane prepared using 1,3,5-cyclohexane tricarboxylicacid chloride for various types of salts. Na₂SO₄ MgSO₄ CaCl₂ NaCl MgCl₂Rejection rate (%) 98.08 ± 0.01 98.34 ± 0.21 92.81 ± 0.49 29.57 ± 1.6895.61 ± 0.52 Membrane Flux 53.72 ± 1.17 55.99 ± 2.28 56.69 ± 0.05 63.06± 0.41 55.23 ± 0.96 (kg · m⁻² · h⁻¹ · MPa⁻¹)

As can be seen from Table 8, as compared to the alicyclic polyamidenanofiltration membrane prepared from 1, 3, 5-cyclohexane tricarboxylicacid chloride and piperazine, the alicyclic polyamide nanofiltrationmembrane prepared from 1, 3, 5-cyclohexane tricarboxylic acid chlorideand trans-1,4-cyclohexanediamine shows a lower monovalent salt rejectionrate. The rejection rate of the divalent salt CaCl₂) is higher than thatof the alicyclic polyamide nanofiltration membrane prepared from 1, 3,5-cyclohexane tricarboxylic acid chloride and piperazine. In particular,the flux for Na₂SO₄ is 53.72 kg·m⁻²·h⁻¹·MPa⁻¹, and the rejection rate is98.08%. At the same time, the rejection rate for the NaCl is 29.57%, andthe flux thereof is 63.06 kg·m⁻²·h⁻¹·MPa⁻¹. Thus, it shows that thestructure of the nanofiltration membrane can be regulated by designingthe molecular structures of the monomers polymerized at the interface,so as to selectively separate the divalent salt from the monovalentsalt. Compared to the trimesoyl chloride and 1, 3-phenylenediaminehaving planar structures, the trans-1, 4-cyclohexanediamine and 1, 3,5-cyclohexane tricarboxylic acid chloride have a twisted conformation.Thus, the nanofiltration membrane prepared therefrom shows a moredeveloped pore structure in the internal structure, which furtherfacilitates Cl⁻¹ going through the nanofiltration membrane, to achievethe selective screening of Cl⁻¹ and SO₄ ²⁻.

Embodiment 9

Preparing the alicyclic polyamide nanofiltration membrane by interfacialpolymerization method, including the following steps:

(1) Soaking a polysulfone ultrafiltration membrane in an alicyclic aminesolution and taking the polysulfone ultrafiltration membrane out after120 s; gas purging the surface of the ultrafiltration membrane to removethe extra alicyclic amine solution. Wherein the alicyclic amine solutionis composed of piperazine and aqueous phase solvent. Wherein the aqueousphase solvent is water. Wherein a mass fraction of the piperazine is 2wt %, and a mass fraction of the aqueous solvent is 98 wt %;

(2) Soaking a 1, 3, 5-cyclohexanetricarboxylic acid chloride solution onthe polysulfone ultrafiltration membrane with the piperazine solution onthe surface obtained in the step (1), and taking the ultrafiltrationmembrane out after 20 s; wherein the organic solvent is iso-Par L.Wherein a mass fraction of the 1, 3, 5-cyclohexanetricarboxylic acidchloride is 0.1 wt %, and a mass fraction of organic solvent is 99.9 wt%;

(3) Providing a heat-treatment to the alicyclic polyamide nanofiltrationmembrane at 60° C. for 120 s, similarly to that of Embodiment 1, toobtain the highly selective alicyclic polyamide nanofiltration membrane.

TABLE 9 Salt rejection properties of the alicyclic polyamidenanofiltration membrane prepared in Embodiment 9 for salts Na₂SO₄ MgSO₄CaCl₂ NaCl KCl Rejection rate (%) 98.27 97.15 67.45 11.57 16.38 Waterflux 93.21 90.25 83.76 97.59 95.25 (kg m⁻² h⁻¹ MPa⁻¹)

As can be seen from Table 9, rejection abilities of the alicyclicpolyamide nanofiltration membrane for different salts are:Na₂SO₄>MgSO₄>CaCl₂)>KCl>NaCl. Specifically, the rejection rate for thedivalent salt Na₂SO₄ is more than 98.27%, while the rejection rate formonovalent salts of NaCl and KCl are respectively 11.57% and 16.38%,showing an excellent selective permeability differences between themonovalent salt and bivalent salt. As to the flux, the fluxes order ofthe alicyclic polyamide membrane to different salts areNaCl>KCl>Na₂SO₄>MgSO₄>CaCl₂, wherein the flux of the monovalent salt isgreater than that of the divalent salt, due to the different radius ofhydration ions of different salt solutions, resulting in osmoticpressure difference on both sides of the diaphragm during infiltration.

The above are only the preferred embodiments of the present inventionand are not intended to limit the present invention. Any modifications,equivalent replacements, improvements, etc. within the spirit andprinciple of the present invention, should be included in the protectionscope of the present invention.

What is claimed is:
 1. A method of making a highly selective alicyclicpolyamide nanofiltration membrane, comprising the steps of: alternatelyand uniformly coating at least an alicyclic acid chloride solution andat least an alicyclic amine solution on a porous support membrane usinga spin coating method or a soaking method for interfacialpolymerization, to form at least one layer of the highly selectivealicyclic polyamide nanofiltration membrane; wherein the soaking methodcomprises alternatively soak-coating the alicyclic acid chloridesolution and the alicyclic amine solution on the porous support membranefor 2-300 s, to form a single layer alicyclic polyamide nanofiltrationmembrane or a multi-layer alicyclic polyamide nanofiltration membrane;the spin coating method comprises alternatively spin-coating thealicyclic acid chloride solution and alicyclic amine solution on theporous support membrane for 2-300 s at 50-10,000 rpm, to form a singlelayer alicyclic polyamide nanofiltration membrane or a multi-layeralicyclic polyamide nanofiltration membrane.
 2. The method of making thehighly selective alicyclic polyamide nanofiltration membrane accordingto claim 1, wherein the interfacial polymerization further comprises thefollowing steps: removing an extra alicyclic acid chloride solution oran extra alicyclic amine solution on the porous support membrane by thespin coating method after an interfacial reaction of the alicyclic acidchloride solution and the alicyclic amine solution, and wherein theextra alicyclic acid chloride solution or the extra alicyclic aminesolution is thrown away at 3,000-10,000 rpm for 2-300 s with a soakingsolvent.
 3. The method of making the highly selective alicyclicpolyamide nanofiltration membrane according to claim 1, wherein aconcentration of the alicyclic acid chloride solution is 0.01-2 wt %, aconcentration of the alicyclic amine solution is 0.01-4 wt %.
 4. Themethod of making the highly selective alicyclic polyamide nanofiltrationmembrane according to claim 3, wherein the alicyclic acid chloridesolution comprises an alicyclic acid chloride, an organic solvent and anadditive; a mass fraction of the alicyclic acid chloride is 0.01-2 wt %,a mass fraction of the organic solvent is 96-99.98 wt % and a massfraction of the additive is 0.01-2 wt %; the organic solvent is one ormore selected from the group consisting of n-hexane, cyclohexane,cyclopentane, n-heptane, n-octane and iso-Par series; and the alicyclicamine solution comprises an alicyclic amine, an aqueous solvent and anadditive; a mass fraction of the alicyclic amine is 0.01-4 wt %, a massfraction of the aqueous solvent is 46-99.98 wt % and a mass fraction ofthe additive is 0.01-50 wt %; and the aqueous solvent is water.
 5. Themethod of making the highly selective alicyclic polyamide nanofiltrationmembrane according to claim 4, wherein the alicyclic amine comprises astructural formula of:

wherein R₁, R₂ are respectively —(CH₂)_(n)— or —NH—, n is 1-3; R₃, R₄,R₅, R₆ are respectively —NH₂ or —CH₃; a number of the —NH— is 1-4, and anumber of the —NH₂ is 1-4; and when a plurality of —NH₂ are on a sameside of a ring, both a cis conformation and a trans conformation areincluded.
 6. The method of making the highly selective alicyclicpolyamide nanofiltration membrane according to claim 4, wherein thealicyclic acid chloride comprises a structural formula of:

wherein A is an alicyclic group selecting from the group consisting offour-membered ring, five-membered ring, six-membered ring,seven-membered ring and eight-membered ring; and R₁, R₂, R₃ and R₄ arerespectively —C(O)Cl group or H, a number of —C(O)Cl group is 3-6, two—C(O)Cl groups are ortho or meta to each other.
 7. The method of makingthe highly selective alicyclic polyamide nanofiltration membraneaccording to claim 1, wherein the porous support membrane is selectedfrom the group consisting of organic polymer ultrafiltration membrane,hollow fiber ultrafiltration membrane, inorganic ultrafiltrationmembrane material and organic-inorganic hybrid porous membrane; theorganic polymer ultrafiltration membrane is selected from the groupconsisting of polysulfone, polyethersulfone, polyacrylonitrile andpolyimide; and the inorganic ultrafiltration membrane material is aporous alumina or a porous ceramic membrane.
 8. A highly selectivealicyclic polyamide nanofiltration membrane, wherein the highlyselective alicyclic polyamide nanofiltration membrane is prepared by amethod comprising the steps of: alternately and uniformly coating atleast an alicyclic acid chloride solution and at least an alicyclicamine solution on a porous support membrane using a spin coating methodor a soaking method for interfacial polymerization, to form at least onelayer of the highly selective alicyclic polyamide nanofiltrationmembrane; wherein the soaking method comprises alternativelysoak-coating the alicyclic acid chloride solution and the alicyclicamine solution on the porous support membrane for 2-300 s, to form asingle layer alicyclic polyamide nanofiltration membrane or amulti-layer alicyclic polyamide nanofiltration membrane; the spincoating method comprises alternatively spin-coating the alicyclic acidchloride solution and alicyclic amine solution on the porous supportmembrane for 2-300 s at 50-10,000 rpm, to form a single layer alicyclicpolyamide nanofiltration membrane or a multi-layer alicyclic polyamidenanofiltration membrane.
 9. The highly selective alicyclic polyamidenanofiltration membrane according to claim 8, wherein the interfacialpolymerization further comprises the following steps: removing an extraalicyclic acid chloride solution or an extra alicyclic amine solution onthe porous support membrane by the spin coating method after aninterfacial reaction of the alicyclic acid chloride solution and thealicyclic amine solution, and wherein the extra alicyclic acid chloridesolution or the extra alicyclic amine solution is thrown away at3,000-10,000 rpm for 2-300 s with a soaking solvent.
 10. The highlyselective alicyclic polyamide nanofiltration membrane according to claim8, wherein a concentration of the alicyclic acid chloride solution is0.01-2 wt %, a concentration of the alicyclic amine solution is 0.01-4wt %.
 11. The highly selective alicyclic polyamide nanofiltrationmembrane according to claim 8, wherein the alicyclic acid chloridesolution comprises an alicyclic acid chloride, an organic solvent and anadditive; a mass fraction of the alicyclic acid chloride is 0.01-2 wt %,a mass fraction of the organic solvent is 96-99.98 wt % and a massfraction of the additive is 0.01-2 wt %; the organic solvent is one ormore selected from the group consisting of n-hexane, cyclohexane,cyclopentane, n-heptane, n-octane and iso-Par series; and the alicyclicamine solution comprises an alicyclic amine, an aqueous solvent and anadditive; a mass fraction of the alicyclic amine is 0.01-4 wt %, a massfraction of the aqueous solvent is 46-99.98 wt % and a mass fraction ofthe additive is 0.01-50 wt %; and the aqueous solvent is water.
 12. Thehighly selective alicyclic polyamide nanofiltration membrane accordingto claim 8, wherein the alicyclic acid chloride solution comprises thealicyclic acid chloride and the organic solvent; the mass fraction ofthe alicyclic acid chloride is 0.01-2 wt %, and the mass fraction of theorganic solvent is 98-99.99 wt %; and the alicyclic amine solutioncomprises the alicyclic amine and the aqueous solvent; the mass fractionof the alicyclic amine is 0.01-4 wt %, and the mass fraction of theaqueous solvent is 96-99.99 wt %.
 13. The highly selective alicyclicpolyamide nanofiltration membrane according to claim 11, wherein theadditive is a nanoparticle, an organic phenol having a distorted spatialstructure, a co-solvent, a hydrophilic additive, a surfactant or whereinthe nanoparticle is selected from the group consisting of flakygraphene, elongated single-walled carbon nanotube, elongatedmulti-walled carbon nanotube, organic spherical porous molecule, andorganic cage-shaped porous molecule; the organic phenol having adistorted spatial structure is5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobiindane orfluorene-9-bisphenol; the co-solvent is selected from the groupconsisting of acetone, polyol, organophosphorus, dimethylsulfoxide anddimethylformamide; the hydrophilic additive is selected from the groupconsisting of quaternary ammonium salt, alcohol-amine, camphorsulfonicacid and polyvinylpyrrolidone (PVP); and the surfactant is one or moreselected from the group consisting of PEG200, PEG400, PEG600, cetyltrimethylammonium bromide, triethylphosphite, camphorsulfonic acidtriethylamine salt, tetrae-thylammonium chloride, and sodium laurylsulfate (SLS).
 14. The highly selective alicyclic polyamidenanofiltration membrane according to claim 8, wherein the alicyclic acidchloride comprises a structural formula of:

wherein A is an alicyclic group selecting from the group consisting offour-membered ring, five-membered ring, six-membered ring,seven-membered ring and eight-membered ring; and R₁, R₂, R₃ and R₄ arerespectively —C(O)Cl group or H, a number of —C(O)Cl group is 3-6, two—C(O)Cl groups are ortho or meta to each other.
 15. The highly selectivealicyclic polyamide nanofiltration membrane according to claim 8,wherein the alicyclic amine comprises a structural formula of:

wherein R₁, R₂ are respectively —(CH₂)_(n)— or —NH—, n is 1-3; R₃, R₄,R₅, R₆ are respectively —NH₂ or —CH₃; a number of the —NH— is 1-4, and anumber of the —NH₂ is 1-4; and when a plurality of —NH₂ are on a sameside of a ring, both a cis conformation and a trans conformation areincluded.
 16. The highly selective alicyclic polyamide nanofiltrationmembrane according to claim 8, wherein the porous support membrane isselected from the group consisting of organic polymer ultrafiltrationmembrane, hollow fiber ultrafiltration membrane, inorganicultrafiltration membrane material and organic-inorganic hybrid porousmembrane; the organic polymer ultrafiltration membrane is selected fromthe group consisting of polysulfone, polyethersulfone, polyacrylonitrileand polyimide; and the inorganic ultrafiltration membrane material is aporous alumina or a porous ceramic membrane.
 17. The method of makingthe highly selective alicyclic polyamide nanofiltration membraneaccording to claim 2, wherein a concentration of the alicyclic acidchloride solution is 0.01-2 wt %, a concentration of the alicyclic aminesolution is 0.01-4 wt %.
 18. The method of making the highly selectivealicyclic polyamide nanofiltration membrane according to claim 17,wherein the alicyclic acid chloride solution comprises an alicyclic acidchloride, an organic solvent and an additive; a mass fraction of thealicyclic acid chloride is 0.01-2 wt %, a mass fraction of the organicsolvent is 96-99.98 wt % and a mass fraction of the additive is 0.01-2wt %; the organic solvent is one or more selected from the groupconsisting of n-hexane, cyclohexane, cyclopentane, n-heptane, n-octaneand iso-Par series; and the alicyclic amine solution comprises analicyclic amine, an aqueous solvent and an additive; a mass fraction ofthe alicyclic amine is 0.01-4 wt %, a mass fraction of the aqueoussolvent is 46-99.98 wt % and a mass fraction of the additive is 0.01-50wt %; and the aqueous solvent is water.